Getting IOError: [Errno Invalid number of channels] -9998 when using mic with PyAudio on Raspberry Pi

问题

Bad news, everyone!

I try to use a microphone on my Raspberry Pi through PyAudio but without success. The microphone is connected to a USB sound card.

The microphone works when I go through 'arecord' :

pi@raspberrypi ~ $ arecord -D plughw:0,0 -f cd test2.wav
Recording WAVE 'test2.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo

However, when I do the test record.py in PyAudio, I got an error. The error is the same for all programs in Python that uses PyAudio :

pi@raspberrypi /usr/src/pyaudio/test $ python record.py 
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
ALSA lib pcm_dmix.c:957:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
Expression 'parameters->channelCount <= maxChans' failed in 'src/hostapi/alsa/pa_linux_alsa.c', line: 1438
Expression 'ValidateParameters( inputParameters, hostApi, StreamDirection_In )' failed in 'src/hostapi/alsa/pa_linux_alsa.c', line: 2742
Traceback (most recent call last):
  File "record.py", line 26, in <module>
frames_per_buffer=CHUNK)
  File "/usr/local/lib/python2.7/dist-packages/pyaudio.py", line 747, in open
stream = Stream(self, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/pyaudio.py", line 442, in __init__
self._stream = pa.open(**arguments)
IOError: [Errno Invalid number of channels] -9998

Thanks for your help

回答1:

Do you have a sound card attached to the Raspberry PI ? By default you get audio output, but not audio input. You can check by running

alsamixer

If you press F6 you should see your sound cards listed. If you press F4 you should see capture devices(if any)

I used a cheap USB soundcard from eBay for testing.

After you have a sound card with an audio input, make sure you configure pyaudio to use the correct sound card index and the number of channels(mine had mono audio input, not stereo).

pyaudio.PyAudio().open(format=pyaudio.paInt16,
                        rate=44100,
                        channels=1, #change this to what your sound card supports
                        input_device_index=1, #change this your input sound card index
                        input=True,
                        output=False,
                        frames_per_buffer=1024)

You can use pyaudio.PyAudio's instance methods get_device_count and get_device_info_by_index to get the indices.

来源：https://stackoverflow.com/questions/31073667/getting-ioerror-errno-invalid-number-of-channels-9998-when-using-mic-with-py

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python

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raspberry-pi2

pyaudio